The present invention relates in general to the measurement of products produced in the tobacco industry and, more particularly, to a method and apparatus for performing on-line measurements of the basis weight of rods of material produced in the tobacco industry by means of a high accuracy, slow response, gauge in combination with a low accuracy, fast response gauge. It is currently preferred to use a low level beta gauge as the high accuracy, slow response gauge and a dielectric sensor as the low accuracy, fast response gauge and, accordingly, the invention will be described herein with primary reference to these preferred gauges.
A beta gauge is commonly used for on-line measurement of rods of material, such as tobacco, in the tobacco industry. One such beta gauge uses a 25 millicurie Strontium 90 radiation source on one side of the rod and an ionization chamber on the opposite side of the rod. Unfortunately, this beta gauge and other known beta gauges require licensing by appropriate nuclear regulatory agencies which impose a number of safety restrictions including, for example, operator training and qualification of safety officers. These regulations make the instruments difficult to ship between factories and countries and also entail high costs of training and maintaining safety officers. In addition, whether real or perceived, there is often a concern over safety and health risks related to regulated nuclear gauging equipment.
In view of these problems with existing gauging devices, there has been an attempt to eliminate nuclear gauging equipment from devices used to measure basis weight in products produced by the tobacco industry. One example is illustrated in U.S. Pat. No. 5,125,418 wherein fibrous material, such as tobacco, is monitored using an optical monitor to determine the mass flow of the solid part of the material. Also the liquid part of the material is monitored by passing the material through a high frequency electric field. Signals representative of the solid part of the material and the liquid part of the material are combined to generate a signal representative of the combined mass flow of the solid and liquid parts which is used to control the basis weight of the material flow. Unfortunately, there are problems associated with this device and it is applicant's understanding that it has not met with commercial success.
Accordingly, there is a need for an improved arrangement for measuring basis weight in rods of material, such as tobacco, produced by the tobacco industry which does not require licensing by nuclear regulatory agencies.